This invention relates generally to the fabrication of integrated circuits on semiconductor wafers, and more particularly to the logistics of moving wafers for processing during fabrication.
A fabrication plant is usually divided into separate areas for particular portions of the fabrication process. Each processing area is called a bay, and each bay contains equipment that is required to process wafers for a certain purpose. In addition to the equipment, material stockers are present near the bay. A material stocker is a large automated cabinet where wafers are stored while waiting to be processed. The wafers are stored in cassettes, and each cassette can hold up to twenty-five wafers. A lot is a logical grouping of wafers in a cassette. The lot can migrate from cassette to cassette as it progresses through the chain of production processes.
A material stocker can hold hundreds of cassettes and services two bays. When a cassette of wafers is ready to be stored in a material stocker, the operator places the cassette at one of the input ports of the material stocker.
When an operator wishes to retrieve a lot from a material stocker, he issues a request via the application program of the host computer. The operator may need empty cassettes to configure or process the wafers. Empty cassettes may be stored in a material stocker, so the operator must have the capability to request empty cassettes. In addition to manipulation of the wafers, the operator may also need to manipulate, or set up, the equipment for an operation.
Once a lot has been retrieved, and the equipment has been set up, the operation on the wafers by a particular piece of equipment, or xe2x80x9ctool,xe2x80x9d can begin. At this point, the lot is xe2x80x9cmoved-inxe2x80x9d to the operation. This state is indicated to the host application by the operator for the lot. The lot remains in this state until the operation is completed. Once the operation is completed, the operator must perform tests and verifications on the wafers. When all tests and verifications have been performed, the host computer application program must be notified. Wafers may have moved from one cassette to another as a result of the operation. The host application has to be notified of this. The operator then places the cassette of xe2x80x9cmoved-outxe2x80x9d wafers in the material stocker, to await orders as to the location of the next piece of equipment which will perform operations on the wafers.
Present automated material handling systems (AMHSs) do not always select the most efficient path for transporting cassettes from one location to another. To illustrate, in many manufacturing environments there are multiple paths by which a cassette may be moved between locations. The paths include physical tracks on which vehicles carry the cassettes, and stockers are present at various locations along the tracks. The length of time required to move a cassette from one location to another is dependent upon the path selected. The reasons for the different transportation times include variations in physical lengths of paths as well as stockers interposed on the tracks between locations. For manufacturing floor efficiency, it is desirable for cassettes to be transported between locations without unnecessary delays.
Present systems are programmed to move a cassette from one location to another such that either a predetermined path is selected or where there are multiple paths, the selection method alternates between the available paths for successive cassettes. If the same path is always selected to moves cassettes, movement delays may occur as a result of too many cassettes being transported on the path. If the system alternates between available paths, some cassettes may be transported very efficiently, while others have relatively long transport times as a result of, for example, physical path length. It would be desirable, therefore, for selection of a path on which to transport a cassette to result in consistently efficient transport times.
The present invention is directed to a system and method for directing the movement of material in a manufacturing environment having a plurality of paths, including at least a first path and a second path, by which the material may be moved. In a first aspect of the invention, a method is provided for routing cassettes in a computer controlled manufacturing arrangement. The method includes the steps of: maintaining an historical record of codes indicative of periods of time expended in transporting cassettes from a first location to a second location via the first path and second path, respectively; determining, as a function of the historical record of codes associated with the paths, which of the first or second paths is more likely to result in a lesser period of time in transporting the cassette; and selecting one of the first or second paths according to which path is more likely to result in a lesser period of time in transporting the cassette.
In another embodiment, the invention is a method that comprises the steps of: measuring periods of time expended in transporting cassettes from a first location to a second location along the first path; measuring periods of time expended in transporting cassettes from the first location to the second location along the second path; associating time period codes indicative of respective measured periods of time with the first and second paths, respectively; in selecting one of the first or second paths for transporting a particular cassette from the first location to the second location, determining, as a function of the time period codes associated with the respective paths, which of the first or second paths is more likely to result in a lesser period of time in transporting the cassette; and selecting one of the first or second paths according to which path is more likely to result in a lesser period of time in transporting the cassette.
An apparatus for selecting either a first or a second path for transporting a cassette from a first location to a second location in an automated manufacturing arrangement is provided in another embodiment of the invention. The apparatus comprises: means for maintaining an historical record of codes indicative of periods of time expended in transporting cassettes from a first location to a second location via the first path and second path, respectively; means for determining, as a function of the historical record of codes associated with the paths, which of the first or second paths is more likely to result in a lesser period of time in transporting the cassette; and means for selecting one of the first or second paths according to which path is more likely to result in a lesser period of time in transporting the cassette.
In another embodiment, the apparatus comprises: means for measuring periods of time expended in transporting cassettes from a first location to a second location along the first path; means for measuring periods of time expended in transporting cassettes from the first location to the second location along the second path; means for associating time period codes indicative of respective measured periods of time with the first and second paths, respectively; means for determining, as a function of the time period codes associated with the respective paths, which of the first or second paths is more likely to result in a lesser period of time in transporting a particular cassette from the first location to the second location; and means for selecting one of the first or second paths according to which path is more likely to result in a lesser period of time in transporting the particular cassette.
A computer controlled manufacturing arrangement with control for selecting between multiple paths for transporting cassettes between processing locations is provided in another aspect of the invention. The manufacturing arrangement comprises: a plurality of stockers interconnected with tracks on which cassettes are carried on vehicles, wherein a first stocker and a second stocker are interconnected by a first path and a second path formed by the tracks; a plurality of robotic arrangements configured to transfer cassettes between the stockers and the vehicles, wherein a first one of the plurality of robotic arrangements is configured to transfer cassettes between the first stocker and vehicles on the first and second paths; and a data processing system coupled to the robotic arrangements and configured and arranged to maintain an historical record of codes indicative of periods of time expended in transporting cassettes from the first stocker to the second stocker via the first path and second path, respectively, to determine, as a function of the historical record of codes associated with the paths, which of the first or second paths is more likely to result in a lesser period of time in transporting the cassette, and to select one of the first or second paths according to which path is more likely to result in a lesser period of time in transporting the cassette.
The above Summary of the Invention is not intended to describe each disclosed embodiment of the present invention.